RICHARDSON'S SKUA. 501 



ingly most strictly accompanies them in their periodical migra- 

 tions. The proximate and final canses of this peculiarity it 

 is difficult to divine." 



It has been a general opinion among the learned that this 

 bird feeds on the dung of Gulls and Terns, whence the name 

 Stercorarius, which they gave it ; the same opinion prevails 

 among the unlearned at the present day, as w^ell as among 

 some of the educated, whence our vernacular names of Dung 

 Bird and Dirten Allen ; but the truth is, as I have satisfied 

 myself by observation, as have many others before me, that it 

 never seizes the mutings, its object being to obtain the undi- 

 gested food of other birds. 



The history of this species is pretty well known, and 

 somewhat fully detailed above ; but the diversity of colour, 

 which seems analogous to that observed in the Buzzards, still 

 requires elucidation. M. Graba having stated that of fifteen 

 individuals killed on their nests, eight white-breasted birds 

 were found to be males, and six brown birds females, assumes 

 it as proved, or at least very probable, that the adult male is 

 white-breasted, and the adult female brown. But others. 

 Dr. Edmondston and INIr. Dunn, for example, have shot 

 white-breasted females, and are well assured that birds of 

 both sexes may be white-breasted, and of both brown-breasted. 

 Analogy would lead to the belief, or probability, that the old 

 birds of both sexes are white-breasted, the middle-aged or 

 adolescent brown. 



Young. — A young bird with its plumage not quite deve- 

 loped, has the bill flesh-coloured for more than half its length, 

 dusky at the end ; the tarsus yellowish-grey ; the toes and 

 webs flesh-coloured, tow^ard the end black ; the claws brown- 

 ish-black. The upper part of the heatl and the hind-neck are 

 pale brownish-yellow, streaked with dusky. The cheeks, 

 throat, and fore neck of a paler tint, more broadly streaked 

 with dusky. The upper parts greyish-black, interruptedly 

 banded with light brownish -red, that colour terminally edging 

 each feather. Quills and tail-feathers deep black, all more 

 or less tipped with light-red, the shafts of several of the pri- 

 maries white. Lower parts dull greyish-yellow, confusedly 



